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Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)[2][3] is the virus that causes coronavirus disease 2019 (COVID-19), the respiratory illness responsible for the COVID-19 pandemic. Colloquially known as simply the coronavirus, it was previously referred to by its provisional name, 2019 novel coronavirus (2019-nCoV),[4][5][6]Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)[2][3] is the virus that causes coronavirus disease 2019 (COVID-19), the respiratory illness responsible for the COVID-19 pandemic. Colloquially known as simply the coronavirus, it was previously referred to by its provisional name, 2019 novel coronavirus (2019-nCoV),[4][5][6][7] and has also been called human coronavirus 2019 (HCoV-19 or hCoV-19).[8][9][10][11] The World Health Organization declared the outbreak a Public Health Emergency of International Concern on 30 January 2020, and a pandemic on 11 March 2020.[12][13]

SARS-CoV-2 is a positive-sense single-stranded RNA virus[14][15] (and hence Baltimore class IV[16]) that is contagious in humans.[17] As described by the US National Institutes of Health, it is the successor to SARS-CoV-1,[10][18] the virus that caused the 2002–2004 SARS outbreak.

Taxonomically, SARS-CoV-2 is a virus of the species severe acute respiratory syndrome-related coronavirus (SARSr-CoV).[2] It is believed to have zoonotic origins and has close genetic similarity to bat coronaviruses, suggesting it emerged from a bat-borne virus.[19][20][21][9] Research is ongoing as of February 2020 as to whether SARS-CoV-2 came directly from bats or indirectly through any intermediate hosts.[22][23] The virus shows little genetic diversity, indicating that the spillover event introducing SARS-CoV-2 to humans is likely to have occurred in late 2019.[24]

Epidemiological studies estimate each infection results in 5.7 new ones when no members of the community are immune and no preventive measures taken.[25] The virus primarily spreads between people through close contact and via respiratory droplets produced from coughs or sneezes.[26][27] It mainly enters human cells by binding to the angiotensin converting enzyme 2 (ACE2).[19][28][29][30]

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